1. Field
The invention is in the field of trailer hitches.
2. State of the Art
Trailer hitches generally used with automobiles and small trucks are usually attached to the rear frame of the towing vehicle with a universal pivot attachment, usually a ball, spaced behind the towing vehicle to pivotally receive thereon a mating attachment, such as a socket, on a tongue extending from the body of the trailer to be towed. This allows easy attachment of the trailer to the towing vehicle and provides good tracking of the trailer around corners and curves negotiated by the towing vehicle.
One problem in towing a trailer is fishtailing. Fishtailing is side to side turning and swaying of the trailer with the trailer pivoting about its pivot connection to the vehicle behind the vehicle. Fishtailing happens primarily with systems having the pivot point of the hitch located behind the towing vehicle between the trailer and the towing vehicle. As the trailer moves from side to side of the towing vehicle, it puts side to side force on the pivot connection between the towing vehicle and the trailer. With the attachment of the hitch to the rear of the towing vehicle body, this tends to cause the rear of the towing vehicle body to start to move or sway from side to side which can lead to loss of control of the vehicle. This is a cyclic motion and frequently causes loss of control of the towed trailer and the towing vehicle. Moving the effective pivot point between the trailer and towing vehicle to the center of the rear axle of the towing vehicle, or ahead of the rear axle to a point between the front and rear axles of the towing vehicle, usually eliminates most of the fishtailing. It is difficult to move or sway a vehicle body to the side in relation to the axles of the vehicle with a side force applied over an axle or between axles. However, it is easier to sway a vehicle body to the side when the side force is applied at the front or rear of the body. A fifth wheel trailer attachment moves the pivot point between the trailer and vehicle over the rear axle of the towing vehicle and provides better stability for the vehicle and trailer combination. However, fifth wheel hitches are not practical for towing trailers with automobiles and small trucks.
Attempts have been made to move the pivot point of a trailer hitch to the rear axle of the towing vehicle. For example, U.S. Pat. No. 5,167,423 shows a trailer hitch attached to the rear axle of a towing vehicle with a drawbar pivotally attached adjacent the rear axle. The drawbar is attached to the trailer in a manner to prevent pivotal movement between the drawbar and the trailer with all pivotal movement occurring at the pivotal mounting of the drawbar adjacent the rear axle of the towing vehicle. While this type of trailer hitch is effective in reducing fishtailing and providing more stability to the vehicle-trailer combination, it has the disadvantage that the tracking of the trailer is changed so that the trailer turns a shorter radius than the rear of the vehicle so cuts corners. Most vehicles on roads, highways, and freeways steer by turning the front wheels of the vehicle. The natural geometry of this steering system causes the rear wheels of the vehicle to track inside the radius of the curve paths of the front wheels. With a trailer pivoted to the towing vehicle adjacent the rear axle, the trailer will track significantly inside the tracks of the rear wheels of the vehicle. The true tracking pivot point for a trailer is midway between the towing vehicle rear wheels and the trailer wheels. Therefore, for tracking purposes, it is advantageous to maintain the trailer pivot point behind the towing vehicle. Also, with the hitch attached to the rear axle of the towing vehicle, the drawbar has to be supported vertically, either by attachment to the rear of the vehicle or to the trailer tongue, so that the trailer connection does not drag on the ground. Further, the rigid attachment of the drawbar to the trailer tongue makes attaching and detaching of the trailer more difficult.
Several trailer hitches have been designed to keep the connection between the towing vehicle and the trailer behind the towing vehicle as with the conventional hitch to provide similar tracking of the trailer and ease of attaching the trailer, but to move the effective pivot point forwardly of the rear of the towing vehicle toward the towing vehicle axle. These hitches generally do not allow any pivotal movement of the trailer tongue about the point of connection to the towing vehicle, although at least one of these hitches allows free pivotal movement of the trailer tongue about the point of connection as with the usual ball and socket connection. Examples of such trailer hitches are shown in U.S. Pat. Nos. 4,019,754, 4,722,542, 5,660,409, 6,305,705, and 3,787,068. However, the need for an improved trailer hitch remains.